St John's Wood

12 screw piles installed for large extension in St John's Wood

Ground Sun was commissioned to work with John Cromer, Arboricultural Consultant, to develop an appropriate method of installing the foundations for a large extension in this prestigious area of north London. Once the scheme was developed and approved by the Council, Ground Sun designed and installed a helical screw pile solution and installed the piles with close liaison and assistance from the Arboricultural Consultant. Careful attention was paid to the tree roots and biodegradable cardboard was installed first using an air lance to a depth of 1 metre where a root was found between the existing tree roots. Ground Sun then installed the screw piles to depths of up to 18 metres. These piles were SS175s with pull down grout column which protects the shaft and ensures the screw pile is both end bearing and friction based.

Access on site was extremely restricted and a 2.4 tonne excavator was the largest piece of machinery that could be brought to site. Ground Sun can install up to 222kN ultimate capacity piles with hydraulic handheld rigs, so access is normally not an issue. However, on this contract the loads were larger at circa 480kN, therefore a small excavator was required. A layer of tree mulch and a steel array of plates were installed and bolted together for stablilty to ensure this excavator did not cause any compaction of the ground whilst installing the piles. This is important as there are many feeder roots in the upper layers and compaction or compression of the ground can damage their health.